1. Field of the Invention
The invention relates to a process for the preparation of a 1,5-benzothiazepine derivative, or a salt thereof, of formula 1 ##STR3## where R.sub.1 represents H, an alkyl group or an alkoxy group and R.sub.2 represents H or a halogen, in which process a propanoic acid derivative of formula 2 ##STR4## where R.sub.1 and R.sub.2 are as defined above and R.sub.3 represents H or an alkyl group, is subjected to an intramolecular cyclisation reaction in a non-halogenated solvent in the presence of a carboxylic acid.
2. Description of Related Art
A process of the same kind is known from Chem. Pharm. Bull. 19, 2028-2037 (1970), in which inter alia acetic acid is mentioned as catalyst in the cyclisation of such propanoic acid derivatives.
A drawback of the known process is that the yield is very low, even at relatively long reaction times.